1. Field of the Invention
This invention relates to a method and apparatus for sealing a well bore by cementing and the like and sidetracking a well from the well bore.
2. Brief Description of Prior Art
Frequently in oil field operations it is necessary to drill wells referred to as "pilot wells" to determine formation properties, formation depths and thicknesses and the like.
These wells may be drilled either as slanted or vertical wells to obtain geologic information prior to drilling a horizontal or other well into a formation of interest. The pilot well permits logging to determine the geologic location of a formation(s) of interest so that the horizontal well can be drilled into a selected location in the formation of interest. Pilot wells may also be used for obtaining information about subterranean formations for use with other types of wells.
Generally, the pilot well is logged to determine the depth and thickness of the various formations penetrated by the pilot well. In the event that the pilot well is not used for production or otherwise it is necessary to plug the pilot well to seal the subterranean formations so that materials from the subterranean formations do not escape to the surface or commingle. This sealing is usually accomplished by cementing the well bore shut. Conventional methods for sealing the well bore involve numerous trips of drill string into the well to complete the cementing operation. As a result the well bore is unavailable for future production and wells for production of fluids based upon the data obtained from the pilot well are drilled to produce fluids from the formation.
Even when the pilot well is used to drill a sidetracked well it is necessary to make numerous trips into the well to complete the cementing operation using conventional methods. Further, it is necessary to make additional trips into the well to place a wedge or other "kickoff" device in the well to enable a drill bit to drill through the hard steel casing when the well has been cased. Alternatively techniques such as milling or the like to open a window in the casing may be used. As a result, the use of such pilot wells for sidetracking is expensive and in many instances these wells are simply abandoned by plugging.
It would be economically desirable to be able to salvage any cased portion of the pilot well and the well bore for use in drilling a sidetracked well. Accordingly, considerable effort has been directed to development of improved and more economical methods and apparatus for sealing the unused portion of a well bore and sidetracking a well from the well bore.